Culture of Bone Biopsy Specimens Overestimates Rate of Residual Osteomyelitis After Toe or Forefoot Amputation

Abstract

Background:Guidelines recommend both histological analysis and culture for definite diagnosis of osteomyelitis. It is not clear if histological and culture criteria can be used interchangeably in the clinical scenario of toe amputation. We therefore prospectively compared the results of intraoperative culture and those of histological examination in this setting.Methods:Consecutive patients requiring toe or forefoot amputation at the University Hospital Basel during a 2-year period were included in the study. Biopsy specimens from the residual bone were cultured according to microbiological standards. Histological analysis was performed using standardized criteria for osteomyelitis. Clinical outcomes were assessed retrospectively via chart review.Results:Of 51 patients included in the study, 33 (65%) had a positive culture of residual bone and 14 (27%) showed histological signs of osteomyelitis. A negative histological result but a positive culture was found for 21 (41%) of the patients, suggesting that culture has a high false-positive rate if histological analysis is used as the reference to rule out osteomyelitis. The recommended criteria of both positive histological findings and positive culture were fulfilled by 12 (24%) of the 51 patients.Conclusions:Positive cultures of residual bone after forefoot or toe amputation overestimate the true rate of osteomyelitis as defined by histological analysis, presumably because of contamination from soft tissue at the time of surgery. Additional studies are needed to evaluate the indications for, and the duration of, antibiotic treatment according to these findings.Clinical Relevance:Our results cast doubt on the strategy of relying solely on culture of bone biopsy specimens when deciding whether antibiotic treatment for osteomyelitis is necessary after toe or forefoot amputation.

Stopping antibiotics after surgical amputation in diabetic foot and ankle infections—A daily practice cohort

“…Likewise, we did not routinely assess residual stump osteomyelitis in patients undergoing atrial amputation. However, recent studies doubt about the accuracy of these specimens, especially when they were sampled through the operation site. Thirdly, it is noteworthy that wound care, especially pressure offloading of the affected limb, is crucial for treating DFI .…”

“…Surgeons in the orthopaedic service do not perform routine microbiological assessment (histology and/or microbiological cultures) of residual bone following amputation and do not use topical antibiotics intraoperatively or on the wounds. 10,11 Specialized nurses provide professional wound care (including minimal debridement) on the ward, specifically dedicated to septic orthopaedic and amputation patients. All patients are actively followed up in our clinical pathway.…”

Guidelines on the diagnosis and treatment of foot infection in persons with diabetes (IWGDF 2019 update)

“…A bone specimen obtained during an operation may be more likely than a percutaneous biopsy to be contaminated from adjoining infected soft tissue. The possibility that many of the positive bone cultures are false positives is supported by the substantially lower rate of positive histology on the same specimen in two studies . Of course, cultures may also be falsely negative, especially in patients treated with antibiotics or when samples are not transported and processed appropriately.…”

“…Several studies have shown that one-third to two-thirds of patients from whom the surgeon obtains a specimen of clinically uninfected bone (variously called "marginal," "distal," or "proximal" bone) after resection have culture or pathological evidence of residual infection. [160][161][162][163][164] This finding presumably means infected bone remains, requiring further antibiotic and/or surgical treatment. It is crucial that the bone specimen be collected as aseptically as possible, including using a new set of sterile instruments.…”

“…The possibility that many of the positive bone cultures are false positives is supported by the substantially lower rate of positive histology on the same specimen in two studies. 160,163 Of course, cultures may also be falsely negative, especially in patients treated with antibiotics or when samples are not transported and processed appropriately. An additional problem is the lack of an agreed definition of osteomyelitis in the diabetic foot.…”